Organosiloxane-silicate copolymer antifreeze composition with nitrate corrosion inhibitor

ABSTRACT

A corrosion-inhibited heat transfer composition concentrate comprising an alcohol, an organosiloxane/silicate copolymer, and a corrosion inhibiting amount of a nitrate salt. Such coolant concentrate may suitably be diluted with from about 25% to about 90% by weight of water based upon the weight of the concentrate, to form an aqueous composition which has particular utility as a corrosion-inhibited heat transfer composition for heat exchange systems, for example, those employed with internal combustion engines. Such compositions are highly effective in reducing corrosion in heat exchange systems containing components of aluminum construction.

This application is a continuation of prior U.S. application Ser. No.802,575, filing date 11/27/85, now U.S. Pat. No. 4,664,833, which is acontinuation-in-part of application Ser. No. 363,829, filing date3/31/82, now abandoned.

FIELD OF THE INVENTION

This invention relates to a corrosion-inhibitive heat transfercomposition comprising alcohol, a water-soluble organosiloxane/silicatecompolymer and a corrosion-inhibiting amount of a nitrate salt.

DESCRIPTION OF THE PRIOR ART

Corrosion-inhibitive heat transfer compositions of aqueous alcoholsolutions heretofore have widely been employed in heat exchange systemsassociated with internal combustion engines, solar systems, and thelike, to depress the freezing point of the coolant water, to raise itsboiling point, and provide corrosion protection.

There are unique corrosion problems associated with the recent trend tothe greater usage of aluminum in internal combustion engine coolingsystems. In such systems, the use of prior art antifreeze/coolantcompositions, which have been formulated for use in cooling systemsconstructed largely of steel, and which have employed corrosioninhibitors for ferrous metal surfaces, fail in many cases to provideadequate corrosion protection for the aluminum structural parts of thecooling system.

The prior art has proposed numerous corrosion-inhibitive heat transfercompositions based on alcohols and employing corrosion inhibitors.Various organic and inorganic inhibitors have been employed. Among theorganic materials which have been utilized are the following: guanidine,citrates, coal tar derivatives, petroleum bases, thiocyanates, peptones,phenols, thioureas, tanin, quinoline, morpholine, triethanolamine,tartrates, glycol monoricinoleate, organic nitrites, mercaptans, organicoils, sulfonated hydrocarbons, fatty oils and soaps. Among the inorganicmaterials which have been employed as inhibitors are sulfates, sulfides,nitrates, fluorides, hydrogen peroxide, alkali metal chromates,nitrites, phosphates, borates, tungstates, molybdates, carbonates, andsilicates and alkaline earth metal borates. Some of these corrosioninhibitors can create difficulties in their use. For example, nitriteshave the tendency to form toxic nitrosamines in amine-containingcompositions.

U.S. Pat. Nos. 3,341,469 and 3,337,496 disclose an aqueous alcoholcomposition employing organosiloxane-silicate copolymers which have beenwidely employed in internal combustion and cooling systems. Thecomposition disclosed in these patents comprises:

an alcohol;

an organosiloxane/silicate copolymer present in an amount of from 0.01percent to 10 percent by weight based upon the weight of saidconcentrate and consisting essentially of:

(1) from 0.1 to 99.9 parts by weight of at least one member selectedfrom the group consisting of (a) siloxane groups represented by theformula:

    RSiO.sub.1.5

wherein R is a member selected from the group consisting of the methyl,ethyl, phenyl and vinyl groups and (b) siloxane groups represented bythe formula: ##STR1## wherein Y is a member selected from the groupconsisting of the cyano group, CH₂ (OH)CH(OH)-group, CH₂ (OH)CH(OH)CH₂-group, ##STR2## CH₂ (OH)CH(OH)CH₂ O-group and R"(OCH₂ CH₂)_(n) (OC₃H₆)_(m) O-group, wherein R" is a member selected from the groupconsisting of the monovalent hydrocarbons and the hydrogen atom, n and mare integers and n has a value of at least 1, m has a value from 0 to 20inclusive, the ratio of n to m is at least 2 to 1, a is an integer andhas a value of at least 2, C_(a) H_(2a) is an alkylene group, the grouprepresented by Y is separated from the silicon atom by at least twosuccessive carbon atoms, b is an integer and has a value of from 1 to 3inclusive, R' is a monovalent hydrocarbon group, c is an integer and hasa value from 0 to 2 inclusive, (b+c) has a value from 1 to 3 inclusive;and

(2) from 0.1 to 99.9 parts by weight of at least one silicate grouprepresented by the formula: ##EQU1## wherein M is a cation that forms awater soluble silicate, d is the valence of the cation represented by Mand has a value of at least 1 and e has a value from 1 to 3 inclusive,said parts by weight of said groups in the copolymer being based on 100parts by weight of the copolymer.

The above described corrosion-inhibitive heat transfer compositions haveenjoyed wide usage. Such composition has superior shelf-life, does notattack rubber parts in cooling systems, is characterized by low levelsof foam formation, and is useful over a wide temperature range evenafter prolonged periods in service.

Despite the foregoing advantages, there exists a continuing need toenhance the corrosion inhibition character of such alcohol andorganosiloxane/silicate copolymer composition to minimize corrosion incooling systems containing aluminum as well as other metals.

Accordingly, it is an object of this invention to provide an improvedcorrosion-inhibitive heat transfer composition comprising alcohol andorganosiloxane/silicate copolymer which is characterized by superiorcorrosion inhibition with respect to aluminum and other materialsstructurally employed in aqueous cooling systems, such as those employedfor internal combustion engines.

SUMMARY OF THE INVENTION

This invention relates in one aspect to an improved corrosion-inhibitiveheat transfer composition concentrate comprising:

(I) an alcohol;

(II) an organosiloxane/silicate copolymer present in an amount of from0.01 percent to 10 percent by weight based upon the weight of saidconcentrate and consisting essentially of:

(1) from 0.1 to 99.9 parts by weight of at least one member selectedfrom the group consisting of (a) siloxane groups represented by theformula:

    RSiO.sub.1.5

wherein R is a member selected from the group consisting of the methyl,ethyl, propyl, phenyl and vinyl groups and (b) siloxane groupsrepresented by the formula: ##STR3## wherein Y is a member selected fromthe groups consisting of halogen containing groups, cyano containinggroups, aryl containing groups, amino containing groups, glycidoxycontaining groups, carboxy ester containing groups, glycidoxy containinggroups, mercapto containing groups, hydroxy and polyhydroxy containinggroups, and mixtures thereof, a is an integer having a value of at least1, the group represented by Y is separated from the silicon atom by atleast two successive carbon atoms, b is an integer having a value offrom 1 to 3 inclusive, R' is a monovalent hydrocarbon group, c is aninteger having a value from 0 to 2 inclusive, (b+c) has a value from 1to 3 inclusive; and

(2) from 0.1 to 99.9 parts by weight of at least one silicate grouprepresented by the formula: ##EQU2## wherein M is a cation that forms awater soluble silicate, d is the valence of the cation represented by Mand has a value of at least 1 and e has a value from 1 to 3 inclusive,said parts by weight of said groups in the copolymer being based on 100parts by weight of the copolymer, the improvement comprising saidcomposition additionally containing at least one nitrate salt, in theabsence of nitrite, in an amount sufficient to provide aluminumcorrosion protection.

Typical "Y" substituents would include, for example,

CF₃, CN, NH₂, Cl, COOH, SH, CH₂ (O)CHCH₂ O, NH₂ CH₂ CH₂ NH, CH₃ OOC, CH₃COO, (CH₂ CH₂ O)_(n), CH₃ OOCCH₂ CH₂ NHCH₂ CH₂ NH, carbohydrates, CH₂(OH)CH(OH), CH₂ (OH)CH(OH)CH₂, ##STR4## CH₂ (OH)CH(OH)CH₂ O, CH₂(OH)CH(OH)CH₂ OCH₂ CH(OH)CH₂ O, CH₂ (OH)CH₂ OCH₂ CH(OH)CH₂ O, R"(OCH₂CH₂)_(n) (OC₃ H₆)_(m) O and R"(OCH₂ CH₂)_(n) (OC₃ H₆)_(m) OCH₂ CH(OH)CH₂O and the like,

wherein R" is a member selected from the group consisting of themonovalent hydrocarbon and the hydrogen atom, and n and m are integershaving a value of from 0 to 20 inclusive.

In another aspect of the invention, the above-describedorganosiloxane/silicate copolymer composition additionally contains from0.1 to 99.8 parts by weight of at least one siloxane group selected fromthe group consisting of the groups represented by the formula:

    R"'SiO.sub.1.5

    R.sub.2 'SiO

and

    R.sub.3 'SiO.sub.0.5

wherein R"' is a monovalent hydrocarbon group other than the methyl,ethyl, propyl, phenyl and vinyl groups and R' has the above-definedmeaning, said parts by weight of said groups in the copolymer beingbased on 100 parts by weight of the copolymer.

In two other embodiments of the invention, there are encompassed theabove compositions additionally containing nitrite in the absence ofphosphate, and nitrite in the absence of borate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above-described corrosion-inhibitive heat transfer concentrate maycontain about 0.1% to about 10% by weight of water, as based upon theweight of the concentrate. Such aqueous concentrate may thereafter inuse be further diluted by addition of from about 25% to about 90% byweight of water based upon the weight of the concentrate, to form acorrosion-inhibitive heat transfer aqueous composition suitable forintroduction into automotive internal combustion engine cooling systems.Both the concentrate and the aqueous composition will generally have apH between about 7 and about 12, preferably between about 8 and about11.

The alcohol employed in the composition of this invention preferably isat least one alcohol selected from the group consisting of methanol,ethanol, propanol, diethylene glycol, triethylene glycol, propyleneglycol, dipropylene glycol, glycerol and ethylene glycol. The preferredalcohol is ethylene glycol.

The nitrate salt employed in the composition of this inventionpreferably is an alkali metal nitrate, more preferably sodium orpotassium nitrate. The nitrate salt is preferably employed in an amountof from about 0.01% to about 1.0% by weight based upon the weight of the(water-free) concentrate, more preferably from about 0.08 to about 0.5weight percent, most preferably from about 0.1 to about 0.3 weightpercent. Below about 0.01 wt.%, the amount of nitrate is expected to beinsufficient to be protective to metals, whereas above about 1.0 wt.%,the cost of the nitrate becomes excessive.

The silicone/silicate copolymer useful in the composition of thisinvention is preferably employed in an amount of from about 0.01% toabout 10% by weight, based upon the weight of the concentrate, morepreferably from about 0.02 weight percent to about 5 weight percent,most preferably from about 0.02 weight percent to about 2 weightpercent, based on the weight of the concentrate. Below about 0.01 wt. %,the amount of siloxane/silicate is expected to be protective to metals,whereas above about 10 wt.%, the cost of the siloxane/silicate becomesexcessive without commensurate improvement in metal corrosion.

The silicate useful in the antifreezes of this invention includesinorganic silicates and organic silicates. Useful inorganic silicatesare represented by the empirical formula: ##EQU3## where M is amonovalent cation that forms a glycol soluble silicate selected from thegroup consisting of sodium, potassium, lithium, rubidium andtetraorganoammonium cations and where w has a value of from 1 to 4inclusive, v has a value from 0 to 3 inclusive and p has a value from 1to 4 inclusive which is equal to the sum of w and v; and

Useful organic silicates are the esters encompassed by the formula:

    Si(OR).sub.4

wherein R is selected from the group consisting of alkyl, aryl,alkoxyalkyl, alkoxyaryl, hydroxyalkoxy, and mixtures thereof. In use,when diluted with water, it is believed that such esters will formsmaller silicate aggregates, which in turn have a greater proficiency ininhibition of metal corrosion as compared to the inorganic silicates.

As illustrative examples of useful inorganic silicates, potassium andsodium silicates are appropriate. Useful organic silicate estersinclude: alkyl silicates such as methyl silicate, ethyl silicate, butylsilicate and amylsilicates; aryl silicates such as benzyl and tolylsilicates; mixed alkyl silicates such as methyl ethyl silicate; mixedaryl silicates such as benzyl tolyl silicate; mixed alkyl aryl silicatessuch as methyl benzyl silicate and ethyl tolyl silicate; glycolsilicates such as hydroxyethyl glycol silicate and hydroxypropyl glycolsilicate; and polyhydroxy alcohol silicates such as glycerol silicateand pentaerythritol silicate; oxyalkylene silicates such as methoxydiethylene glycol silicate, i.e. METHYL CARBITOL® silicate; and mixturesof the above. The preferred organic silicate is tetra-hydroxyethoxyorthosilicate. Also useful within the scope of the present invention isthe well-known class of partially condensed orthosilicate esters.

The amount of silicate in the concentrates used to make the antifreezesof this invention can vary over a wide range, as has been discussed, butis preferably present in an amount of between 100 and 700 ppm ofequivalent Si, more preferably in an amount between 300 and 500 ppm.Below 100 ppm, insufficient silicate would generally be provided tominimize metal corrosion inhibition in the automobile cooling system,whereas above 700 ppm, silicate gels may be encountered in theantifreeze concentrate. Gelation is undesirable because the silicates inthe gel are not available to protect the metal surfaces of theautomotive cooling system but rather are aggregated in the gel itself.

The starting silicate used in producing the copolymers useful in thisinvention can be added to the reaction mixture as such or it can beformed in situ by adding the appropriate hydroxide (e.g. NaOH or KOH)and a silica to the reaction mixture.

The copolymers useful in the present invention can be formed in situ inthe antifreeze formulation by mixing organosilanes with silicates in thepresence of the alcohol being employed. The process of making copolymersuseful in the present invention is well known in the art and isdisclosed, for example, in U.S. Pat. No. 3,337,496 incorporated hereinby reference. The preferred copolymers comprise 0.1 to 40 parts byweight of siloxane and 60 to 99.9 parts by weight of silicate, saidparts by weight being based upon silicon equivalents.

Optional additives may be employed in minor amounts of less than 50 wt.percent based on the weight of the aqueous composition. Typical optionaladditives would include, for example, known corrosion inhibitors formetals such as, for example, tungstates, selenates, chromates,carbonates and bicarbonates, sebacates and other dicarboxylic acids,molybdates, borates, phosphates and benzoates, hydroxy benzoates oracids thereof, silicones, alkali metal nitrates, alkali metal nitrites,tolyltriazole, mercaptobenzothiazole, benzotriazole, and the like, ormixtures thereof. If one or more of the known inhibitors are employedtogether with the inhibitors of the present invention, the sum total ofall inhibitors should be used in an "inhibitory effective amount", i.e.,an amount sufficient to provide some corrosion inhibition with respectto the aluminum surfaces to be protected. Other typical optionaladditives would include buffers, such as alkali metal borates,phosphates and carbonates; wetting agents and surfactants such as, forexample, known ionic and non-ionic surfactants such as thepoly(oxyalkylene) adducts of fatty alcohols; antifoams and/or lubricantssuch as the well-known polysiloxanes and the polyoxyalkylene glycols, aswell as any other minor ingredients known in the antifreeze art.

The following example is merely illustrative of, and not intended tolimit, the present invention.

EXAMPLE 1 ELECTROCHEMICAL TESTS SHOWING EFFECTIVENESS OF NITRATE WITHSILICONE/SILICATE COPOLYMER

In order to test an automobile coolant composition for effectivenesswith and without the use of nitrate, several compositions wereformulated, as identified in Table I below. The base fluid consisted ofan aqueous borate-phosphate glycol composition.

The composition of each of the fluids, together with the respective pHsand ASTM reserve alkalinities (RA), is given in Table I.

                                      TABLE I                                     __________________________________________________________________________    Test Fluid Compositions, pHs and Reserve Alkalinity (RA)                                           Potassium                                                         Borax  NaOH Silicate                                                                            NaNO.sub.3                                                                         Silicone.sup.(c)                                                                    H.sub.3 PO.sub.4                                                                   pH   ASTM                          Fluid #  5 Mole aq..sup.(d)                                                                   50% aq.                                                                            50%(b) aq.                                                                          40% aq.                                                                            A     75% aq.                                                                            33% aq.                                                                            RA                            __________________________________________________________________________    1 (Base Fluid)                                                                         0.3975 0.1858                                                                             --    --   --    0.6602                                                                             (a)  (a)                           2        0.3975 0.9942                                                                             --    --   0.0775                                                                              0.6602                                                                             10.12                                                                              11.90                         3        0.3975 0.1858                                                                             --    0.50 --    0.6602                                                                             (a)  (a)                           4        0.3975 0.1858                                                                             --    0.50 0.0775                                                                              0.6602                                                                             (a)  (a)                           5        0.3975 0.9942                                                                             0.3887                                                                              --   --    0.6602                                                                              9.85                                                                              12.65                         6        0.3975 0.9942                                                                             0.3887                                                                              --   0.0775                                                                              0.6602                                                                              9.85                                                                              12.57                         7        0.3975 0.9942                                                                             0.3887                                                                              0.5  --    0.6602                                                                             10.02                                                                              12.64                         8 (Present                                                                             0.3975 0.9942                                                                             0.3887                                                                              0.5  0.0775                                                                              0.6602                                                                              9.84                                                                              12.75                           Invention)                                                                  __________________________________________________________________________     (a)Nominal pH of 10 and RA of 12                                              (b)0.3418% Kasil 6 (PQ Corporation) + 0.469% NaOH 50 wt. % aqueous             .sup.(c) Silicone A is defined in Table II below.                            .sup.(d) "aq." denotes aqueous throughout this table.                    

Each of the compositions given in Table II below was subjected tostandard potentiodynamic anodic polarization tests using a PrincetonApplied Research Model 350 testing apparatus to give two values on apure aluminum sample, namely the general surface corrosion value for agiven fluid (I_(Corr)) and the tendency to pit value (E_(Br)). The testswere conducted at room temperature with agitation of each of thecompositions.

The results are given in Table II below:

                  TABLE II                                                        ______________________________________                                        ELECTROCHEMICAL DATA                                                                                           I.sub.Corr                                   pH  Fluid #  Key Components      (nA/cm2)                                                                             E.sub.Br                              ______________________________________                                        10  1        BASE FLUID          5,000  1.3                                   10  2        SILICONE A*         5,317  1.4                                   10  3        NITRATE             5,600  1.7                                   10  4        SILICONE A*, NITRATE                                                                              8,542  1.5                                   10  5        SILICATE              670  1.3                                   10  6        COPOLYMER A**         596  1.2                                   10  7        SILICATE, NITRATE   1,190  1.8                                   10  8        COPOLYMER A**, NITRATE                                                                              700  1.7                                   ______________________________________                                         *Silicone A is an organosiloxane within the scope of this invention made      from a silane having the structural formula: CH.sub.3 O(CH.sub.2 CH.sub.2     O).sub.7.2 C.sub.3 H.sub.6 Si(OCH.sub.3).sub.3.                               **Copolymer A is a copolymer of the invention consisting of the reaction      product of the Silicone A and potassium silicate as detailed in Table I. 

The results, as given in Table II above, indicate that, for a givencomposition, the addition of nitrate provides a reduction in thetendency to pit as measured by an increase in the E_(Br) value (comparethe E_(Br) value of fluid #2 with fluid #4; fluid #5 with fluid #7 andfluid #6 with fluid #8). The silicate provides a reduction in thegeneral surface corrosion as measured by a decrease in the I_(Corr)value. The silicone alone, as employed in fluid #2, shows no improvementin either tendency to pit or surface corrosion rate as compared to thebase fluid #1. The combination of silicate and nitrate showed a highgeneral surface corrosion rate (I_(Corr)) and a low tendency to pit(E_(Br)) refer to fluid #7 in Table II.

The testing of fluid #8, in contrast, showed an unexpected improvement.The combination of nitrate with silicone/silicate provides a minimalgeneral surface corrosion rate, as indicated by the very low I_(Corr)shown for fluid #8 of Table I, and a surprisingly effective protectionagainst pit corrosion, as indicated by the high E_(Br) value.

Thus, Fluid #8 gives surprisingly effective performance, especially ascompared to the performance of fluid #2 and fluid #7, most notably withregard to I_(Corr). Fluid #2 containing silicone A provided an I_(Corr)of 5,317, and fluid #7 provided an I_(Corr) of 1,190. However, whenthese three components are combined containing silicate and nitrate in asingle fluid (fluid #8) the I_(Corr) dropped down to 700. This decreasewas unexpected. This combination of favorable I_(Corr) and E_(Br) valuesindicates that fluid #8 will provide excellent corrosion resistance inan engine cooling system.

EXAMPLE 2 ELECTROCHEMICAL TESTS ON COMPOSITIONS WITHIN THE SCOPE OF THEPRESENT INVENTION COMPARED TO A PRIOR ART COMPOSITION CONTAININGNITRITE, PHOSPHATE AND BORATE PLUS SILICONE/SILICATE AND NITRITE

Additional formulations were prepared and tested in the apparatusidentified in Example 1 above using pure aluminum test specimens.

Formulations A through F were prepared having the ingredients describedin Table III. In this regard, it should be noted that formulations B, Dand F contain no nitrite, and formulations E and F contain no borate.The formulations were prepared to provide a basis for a side-by-sideelectrochemical test comparison between several compositions (B throughF) within the scope of the present invention and a composition notwithin the scope of the present invention containing phosphate, borate,nitrate, and nitrite, namely formulation A, a prior art composition.

In addition to measurements of the I_(Corr) and E_(Br) described above,a measurement was made of the "pitting parameter". The pitting parameteris a measure of the total pitting on the surface of an aluminum specimenmeasured in accordance with the procedure described hereinbelow. Each ofthe above measures of corrosion is well known to those skilled in theart and in terms of relative importance, I_(Corr) is considered by theart to be more important than the pitting parameter which in turn isconsidered to be more important than the E_(Br).

                                      TABLE III                                   __________________________________________________________________________    Electrochemical Test Solution Compositions                                                  Weight-% of Each Component                                      Formulation:  A (Comparison)                                                                        B   C   D   E   F                                       __________________________________________________________________________    Base          96.4    96.9                                                                              97.3                                                                              98.8                                                                              95.4                                                                              95.9                                    (Ethylene Glycol)                                                             Borate        0.4     0.4 0.8 0.8 --  --                                      (Na.sub.2 B.sub.4 O.sub.7.5H.sub.2 O)                                         NaOH (50%)    1.0     1.0 0.4 0.4 1.7 1.7                                     H.sub.3 PO.sub.4 (75%)                                                                      0.7     0.7 --  --  1.4 1.4                                     Polyethylene oxide                                                                          0.1     0.1 0.1 0.1 0.1 0.1                                     propyl trimethoxy-                                                            silane (having an                                                             average of 7 EO groups                                                        per molecule)                                                                 Potassium Silicate                                                                          0.3     0.3 0.3 0.3 0.3 0.3                                     NaOH (50 wt. % aqueous)                                                                     0.1     0.1 0.1 0.1 0.1 0.1                                     NaNO.sub.3 (40 wt. % aqueous)                                                               0.5     0.5 0.5 0.5 0.5 0.5                                     NaNO.sub.2 (40 wt. % aqueous)                                                               0.5     --  0.5 --  0.5 --                                                    100.0   100.0                                                                             100.0                                                                             100.0                                                                             100.0                                                                             100.0                                   pH (33 wt. % aqueous)                                                                       10.2    10.2                                                                              9.9 9.9 9.8 9.8                                     RA (ASTM)     13.0    12.6                                                                              13.6                                                                              13.0                                                                              12.4                                                                              12.1                                    __________________________________________________________________________

Each of the formulations described in Table III above was tested todetermine I_(Corr) and pitting parameters on the Princeton AppliedResearch Model 350 testing apparatus to determine these corrosionparameters on a pure aluminum test specimen.

As has been noted above, I_(Corr) and the pitting parameters areconsidered to be more significant than the E_(Br) value. E_(Br) was onlymeasured for formulations A and B, and was found to be comparable forthese formulations at 2.1 and 2.2 E_(Br) values, respectively. Theresults, in terms of I_(Corr) and pitting parameter values, are given inTable II below for each of the formulations.

                  TABLE IV                                                        ______________________________________                                        Electrochemical Test Results                                                  on PAR Model 350 Testing Apparatus                                                             Icorr                                                        Formulation      (nA/cm 2) Pitting                                            ______________________________________                                        A      (Comparison)  500       0.032                                          B                    500       0.005                                          C                    120       0.051                                          D                     34       0.062                                          E                     25       0.018                                          F                     63       0.004                                          ______________________________________                                    

The results presented in Table IV show formulations C through F of thepresent invention to be superior to that of prior art formulation A, onthe basis of Icorr alone. Icorr represents the total metal corrosion andthis parameter is of paramount importance in the assessment ofcorrosion, as for example discussed in the publication Corrosion andCorrosion Control by Herbert H. Uhlig (Second Edition, 1971), pps. 14and 39. Uhlig describes pitting as an attack on an area of metal actingas an anode, whereas I_(Corros) is described as the corrosion rate ofanodic areas of a metal surface (see pages 14 and 39, respectively ofUhlig). Hence, as explained by the Uhlig I_(Corr) is a total metalcorrosion parameter, of which pitting is only one part. The pittingparameter (total pitting measurement) shows formulation B to be superiorto that of formulation A.

EXAMPLE 3 ELECTROCHEMICAL TESTS ON COMPOSITIONS WITHIN THE SCOPE OF THEPRESENT INVENTION SHOWING THE CORROSION-INHIBITIVE PERFORMANCE ONALUMINUM OF VARIOUS SILICONES, AND SILICONE TO SILICATE RATIOS, AS WELLAS VARIOUS NITRATE LEVELS

Still further formulations were prepared and tested on the testingapparatus described in Example 1 above. In the present example, severaldifferent silicones within the scope of the present invention asdescribed in Table V were tested to determine the I_(corr) and pittingparameter values for each formulation on the Princeton Applied ResearchModel 350 testing apparatus using a pure aluminum test specimen. It isnoted that formulation H was diluted to 33 wt.% aqueous and heated to100° C. and maintained at that temperature overnight before testing. Theother formulations were prepared and tested immediately thereafter.

                                      TABLE V                                     __________________________________________________________________________    Electrochemical Test Solution Compositions                                                  Weight-% Of Each Component                                      Formulation:  G    H    I    J    K                                           __________________________________________________________________________    Base (Ethylene Glycol)                                                                      97.2632                                                                            96.4427                                                                            92.0447                                                                            96.2632                                                                            93.7632                                     Borate        0.3975                                                                             0.3975                                                                             0.3975                                                                             0.3975                                                                             0.3975                                      (Na.sub.2 B.sub.4 O.sub.7 5H.sub.2 O)                                                       0.3975                                                                             0.3975                                                                             0.3975                                                                             0.3975                                                                             0.3975                                      NaOH (50%)    0.9936                                                                             0.9936                                                                             1.1370                                                                             0.9936                                                                             0.9936                                      H.sub.3 PO.sub.4 (75%)                                                                      0.6602                                                                             0.6602                                                                             0.6602                                                                             0.6602                                                                             0.6602                                      Silicone:                                                                     NC C.sub.2 H.sub.4 Si(OEt).sub.3                                                            0.0006                                                                             --   --   0.0006                                                                             0.0006                                      CH.sub.3 COOC.sub.2 H.sub.4 Si(OEt).sub.3                                                   --   0.5560                                                                             0    --   --                                          HCOC.sub.2 H.sub.4 Si(OEt).sub.3                                                            --   --   0.9990                                                                             --   --                                          MeO(EO).sub.20 (CH.sub.2).sub.3 Si(OMe).sub.3                                               --   --   3.9960                                                                             --   --                                          Sodium Silicate*                                                                            0.3727                                                                             0.0015                                                                             0.0133                                                                             0.3727                                                                             0.3727                                      NaOH (50 wt. % aqueous)                                                                     0.0622                                                                             0.0002                                                                             0.0023                                                                             0.0622                                                                             0.0622                                      H.sub.2 O     --   0.1983                                                                             --   --   --                                          NaNO.sub.3 (40 wt. % aqueous)                                                               0.2500                                                                             0.7500                                                                              0.7500                                                                             1.2500                                                                             3.7500                                     Total         100.0000                                                                           100.0000                                                                           100.0000                                                                           100.000                                                                            100.000                                     pH (33 wt. % aqueous)                                                                       9.9  9.9  10.2 9.9  9.9                                         RA (ASTM)     13.2 12.4 13.0 13.2 13.2                                        __________________________________________________________________________     *PQ "N", a product of PQ Corporation.                                    

                  TABLE VI                                                        ______________________________________                                        Electrochemical Test Results on                                               PAR Model 350 Testing Apparatus                                                         wt %      I.sub.Corr                                                Formulation                                                                             NaNO.sub.3                                                                              (nA/cm 2) Pitting Parameter                               ______________________________________                                        G         0.1       190       0.002                                           H         0.3        30       0.025                                           I         0.3        90       0.003                                           J         0.5        90       -0.00075                                        K         1.0       260       -0.0024                                         ______________________________________                                    

As can be readily seen from the data in Table VI, the I_(Corr) andpitting parameter values fall within the ranges obtained forformulations C through F as given in Table V. The values of I_(Corr) andpitting parameter represent reduced corrosion as compared to thecorresponding results for formulation A given in Table IV. It isparticularly noteworthy that these excellent results are achieved usinga formulation having very low silicone to silicate ratio of about 1 to999 (formulation G) and also very high silicone to silicate ratio of 999to 1 (formulation H). In addition to testing this range of silicone tosilicate ratios, various silicones were utilized as identified in TableV.

Also tested were several nitrate amounts that calculate to be 0.1 wt.%(formulation G); 0.3 wt.% (formulations H and I); 0.5 wt.% (formulationJ); and 1.0 wt.% (formulation K) of nitrate based on the total weight ofthe composition. Effective total metal corrosion inhibition was providedover this range of nitrate amounts as is demonstrated by the lowI_(Corr) values provided by formulations G through K.

We claim:
 1. An improved method for protecting from corrosion anautomobile internal combustion engine cooling system with acorrosion-inhibitive heat transfer composition concentrate wherein saidmethod comprises diluting said concentrate with from about 15 to about90 percent by weight of water, based on the weight of the concentrateand introducing such to an automobile internal combustion engine coolingsystem, said concentrate comprising:(I) an alcohol; (II) anorganosiloxane/silicate copolymer present in an amount from 0.01 percentto 10 percent by weight based upon the weight of said concentrate andconsisting essentially of:(1) from 0.1 to 99.9 parts by weight of atleast one member selected from the group consisting of (a) siloxanegroups represented by the formula:

    RSiO.sub.1.5

wherein R is a member selected from the group consisting of the methyl,ethyl, propyl, phenyl and vinyl groups and (b) siloxane groupsrepresented by the formula: ##STR5## wherein Y is a member selected fromthe groups consisting of halogen containing groups, cyano containinggroups, aryl containing groups, amino containing groups, carboxycontaining groups, carboxy ester containing groups, glycidoxy containinggroups, mercapto containing groups, hydroxy and polyhydroxy containinggroups, and mixtures thereof, a is an integer having a value of at least2, the group represented by Y is separated from the silicon atom by atleast two successive carbon atoms, b is an integer having a value from 1to 3 inclusive, R' is a monovalent hydrocarbon group, c is an integerhaving a value from 0 to 2 inclusive, (b+c) has a value from 1 to 3inclusive; and (2) from 0.1 to 99.9 parts by weight of at least onesilicate group represented by the formulae and mixtures thereof:##EQU4## wherein M is a cation that forms a water soluble silicate, d isthe valence of the cation represented by M and has a value of at least 1and e has a value from 1 to 3 inclusive,

    Si(OR).sub.4                                               (B)

wherein R is selected from the group consisting of alkyl, aryl,alkoxyalkyl, alkoxyaryl, hydroxyalkoxy, and mixtures thereof, said partsby weight of said groups in the copolymer being based on 100 parts byweight of the copolymer, and (III) at least one nitrate salt, in theabsence of nitrite, present in an amount of from about 0.08 to about 0.5weight percent based on the total weight of the composition.
 2. Theimproved method of claim 1 wherein the nitrate in the concentrate ispresent on an amount of from about 0.1 to about 0.3 weight percent basedon the total weight of the composition.
 3. An improved method forprotecting from corrosion an automobile internal combustion enginecooling system with a corrosion-inhibitive heat transfer compositionconcentrate wherein said method comprises diluting said concentrate fromabout 25 to about 90 percent by weight of water, based on the weight ofthe concentrate, and introducing the diluted concentrate to anautomobile internal combustion engine cooling system wherein saidconcentrate comprising:(I) an alcohol; (II) an organosiloxane/silicatecopolymer present in an amount of from 0.01 percent to 10 percent byweight based upon weight of said concentrate and consisting essentiallyof:(1) from 0.1 to 99.9 parts by weight of at least one member selectedfrom the group consisting of (a) siloxane groups represented by theformula:

    RSiO.sub.1.5

wherein R is a member selected from the group consisting of the methyl,ethyl, propyl, phenyl and vinyl groups and (b) siloxane groupsrepresented by the formula: ##STR6## wherein Y is a member selected fromthe group consisting of halogen containing groups, cyano containinggroups, aryl containing groups, amino containing groups, carboxycontaining groups, glycidoxy containing groups, mercapto containinggroups, hydroxy and polyhydroxy containing groups, and mixtures thereof,a is an integer having a value of at least 2, the group represented by Yis separated from the silicon atom by at least two successive carbonatoms, b is an integer having a value from 1 to 3 inclusive, R' is amonovalent hydrocarbon group, c is an integer having a value from 0 to 2inclusive, (b+c) has a value from 1 to 3 inclusive; and (2) from 0.1 to99.9 parts by weight of at least one silicate group represented by theformulae and mixtures thereof: ##EQU5## wherein M is a cation that formsa water soluble silicate, d is the valence of the cation represented byM and has a value of at least 1 and e has a value from 1 to 3 inclusive,

    Si(OR).sub.4                                               (B)

wherein R is selected from the group consisting of alkyl, aryl,alkoxyalkyl, alkoxyaryl, hydroxyalkoxy, and mixtures thereof, said partsby weight of said groups in the copolymer being based on 100 parts byweight of the copolymer, (III) a borate in the absence of phosphate, and(IV) a nitrate present in an amount of from about 0.08 to about 0.5weight percent based on the total weight of the composition.
 4. Animproved method for protecting from corrosion an automobile internalcombustion engine cooling system with a corrosion-inhibitive heattransfer composition concentrate wherein said method comprises dilutingsaid concentrate with from 25 percent to about 90 percent by weight ofwater based on the weight of the concentrate, an introducing the dilutedconcentrate to an automobile internal combustion engine cooling systemwherein said concentrate comprising:(I) an alcohol; (II) anorganosiloxane/silicate copolymer present in an amount of from 0.01percent to 10 percent by weight based upon the weight of saidconcentrate and consisting essentially of:(1) from 0.1 to 99.9 parts byweight of at least one member selected from the group consisting of (a)siloxane groups represented by the formula:

    RSiO.sub.1.5

wherein R is a member selected from the group consisting of the methyl,ethyl, propyl, phenyl and vinyl groups and (b) siloxane groupsrepresented by the formula: ##STR7## wherein Y is a member selected fromthe groups consisting of halogen containing groups, cyano containinggroups, aryl containing groups, amino containing groups, carboxycontaining groups, carboxy ester containing groups, glycidoxy containinggroups, mercapto containing groups, polyhydroxy containing groups, andmixtures thereof, a is an integer having a value of at least 2, thegroup represented by Y is separated from the silicon atom by at leasttwo successive carbon atoms, b is an integer having a value of from 1 to3 inclusive, R' is a monovalent hydrocarbon group, c is an integerhaving a value from 0 to 2 inclusive, (b+c) has a value from 1 to 3inclusive; and (2) from 0.1 to 99.9 parts by weight of at least onesilicate group represented by the formulae and mixtures thereof:##EQU6## wherein M is a cation that forms a water soluble silicate, d isthe valence of the cation represented by M and has a value of at least 1and e has a value from 1 to 3 inclusive,

    Si(OR).sub.4                                               (B)

wherein R is selected from the group consisting of alkyl, aryl,alkoxyalkyl, alkoxyaryl, hydroxyalkoxy, and mixtures thereof, said partsby weight of said groups in the copolymer being based on 100 parts byweight of the copolymer, (III) a phosphate in the absence of borate,(IV) a nitrate present in an amount of from about 0.08 to about 0.05weight percent based on the total weight of the composition.
 5. Themethod of any of claims 1 through 4 wherein said Y in said compositionconcentrate is selected from the group consisting of carbohydrates,CF₃,CN, NH₂, Cl, COOH, SH, CH₂ (O)CHCH₂ O, NH₂ CH₂ CH₂ NH, CH₃ OOC, CH₃COO(CH₂ CH₂ O)_(n), CH₃ OOCCH₂ CH₂ NHCH₂ CH₂ NH CH₂ (OH)CH(OH), CH₂(OH)CH(OH)CH₂, ##STR8## CH₂ (OH)CH(OH)CH₂ O, CH₂ (OH)CH(OH)CH₂ OCH₂CH(OH)CH₂ O, CH₂ (OH)CH₂ OCH₂ CH(OH)CH₂ O, R"(OCH₂ CH₂)_(n) (OC₃ H₆)_(m)O, and R"(OCH₂ CH₂)_(n) (OC₃ H₆)_(m) OCH₂ CH(OH)CH₂ O group, and thelike,wherein R" is a member selected from the group consisting of themonovalent hydrocarbon and the hydrogen atom, and n and m are integershaving a value of from 0 to 20 inclusive.
 6. The method of any of claims1 through 4 wherein said organosiloxane/silicate copolymer additionallycontains from 0.1 to 99.8 parts by weight of a siloxane group selectedfrom the group consisting of the groups represented by the formulae:

    R"'SiO.sub.1.5

    R.sub.2 'SiO

and

    R.sub.3 'SiO.sub.0.5

wherein R"' is a monovalent hydrocarbon group other than the methyl,ethyl, phenyl and vinyl groups and R' has the above-defined meaning,said parts by weight of said groups in the copolymer being based on 100parts by weight of the copolymer.
 7. The method of any of claims 1through 4 wherein said composition concentrate additionally containswater in an amount sufficient to form a corrosion-inhibitive heattransfer composition.
 8. The method of any of claims 1 through 4 whereinsaid composition concentrate additionally contains carbonate or sebacateor a mixture thereof.
 9. The method of any of claims 1 through 4 whereinsaid organosiloxane/silicate copolymer comprises 0.1 to 40 parts byweight of siloxane and 60 to 99.9 parts by weight of silicate, saidparts by weight being based upon silicone equivalents.